This study compared cross-language speech perception of vowel length contrasts in Arabic and Japanese by two groups of listeners whose first language (L1) was either Cantonese (C) or Korean (K). Unlike Arabic or Japanese, C and K do not use vowel length contrastively. One group (CK+J) had experience learning Japanese as a foreign language while the other (CK) did not. The question of interest was if Japanese learning experience separated the two groups in their perception of Arabic as well as Japanese vowel length contrasts. The effect of learning Japanese was negligible for CK+J who participated in this study. Further, it appeared that learning Japanese had a somewhat negative effect on the listeners’ perception of Arabic contrasts. The pattern of results obtained may reflect a temporary and transient nature of listeners’ interlanguage and has implications for adults’ speech learning capabilities.